1. Field of the Invention
This invention relates to a radiation-sensitive resin composition containing an alkali-soluble resin. More particularly, this invention relates to a radiation-sensitive resin composition suited for a photoresist used for fabricating integrated circuits, that is well sensitive to a variety of radiations including ultraviolet radiations such as g-rays and i-rays, far-ultraviolet radiations such as KrF excimer laser beams, X-radiations such as synchrotron rays, and charged-particle radiations such as electron rays, and particularly sensitive to ultraviolet radiations and far-ultraviolet radiations.
2. Description of the Prior Art
Positive photoresists are widely used in the fabrication of integrated circuits. As integrated circuits have become more highly integrated in recent years, it is desired to provide positive photoresists that enables formation of photoresist patterns more improved in resolution.
To improve photoresist materials commonly for the purpose of improving the resolution of positive photoresists, a method is available in which e.g., alkali-soluble resins used in photoresists are made to have a low molecular weight. This method, however, may cause a problem that the photoresists may have a low heat resistance. Another method is also available in which, as an approach from process improvement, the numerical aperture (NA) of a stepper is made greater for improving the resolution. This method, however, may cause a problem of resulting in a narrow focal depth (focal latitude), and hence simultaneously requires an improvement of the photoresist material. For example, in order to improve the focal latitude, one of measures therefor is to add a quinonediazide compound in a larger quantity. However, the addition of the quinonediazide compound in a larger quantity results in a poor developability. Thus, in the positive photoresists, an improvement in one performance brings about a lowering of another performance. Accordingly, it is required to provide a positive photoresist simultaneously having a high resolution, a good focal latitude and a good developability in a fine pattern.
For example, Japanese Pre-examination Patent Publication (kokai) No. 8-262710 discloses a positive photoresist composition containing (A) an alkali-soluble resin obtained by subjecting at least one phenol compound represented by the following general formula (I) and at least one phenol compound other than the phenol compound of the formula (I) to condensation with an aldehyde in the presence of an acid catalyst and (B) a quinonediazidosulfonic acid ester radiation-sensitive agent. ##STR2##
wherein R.sub.1 represents a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group or a substituted or unsubstituted aryl group; and R.sub.2 to R.sub.6 each independently represent a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group or a substituted or unsubstituted cycloalkyl group, and any one of R.sub.2, R.sub.4 and R.sub.6 is a hydrogen atom provided that two or more of them are not hydrogen atoms at the same time. As the alkali-soluble resin, the publication specifically discloses a resin obtained by condensation of a combination of 2,6-dimethylphenol and a phenol other than the phenol compound of the general formula (I), e.g., m-cresol, with an aldehyde.
However, the positive photoresist composition disclosed therein has insufficient performances in respect of resolution, developability, heat resistance, pattern shape, exposure margin and focal latitude, and also has a problem that these performances are ill balanced.